1. Field of the Invention
The invention relates to a method and apparatus for drawing out a thread chain reliably and smoothly on a sewing machine of a type which forms multiple-needle stitches (U.S. Federal Standard stitch type 406 or 407) by at least two needles and one looper, and a novel thread chain that can be formed by the sewing machine of this type.
2. Description of the Prior Art
In a sewing machine of a type which forms stitches by using multiple needles and one looper, such as a multiple-needle, double chain stitch sewing machine which does not use a upper cover thread, it is essential to form a thread chain smoothly between consecutive fabrics in order to feed the fabrics one after another and sew intermittently by continuous operation of the sewing machine.
In conventional sewing machines of the above type, however, after sewing one fabric, the thread chain linked to the sewing end is pushed down beneath the throat plate as the needles descend, and therefore, in the next step, when the looper goes out to pick up the needle thread loop, it simultaneously hooks the pressed-down thread chain, and the thread chain cannot be delivered. Moreover, the right and left needle threads cannot maintain a specific interval therebetween unless there is a fabric for sewing, and are unable to form uniform stitches, thereby making it impossible to draw out and deliver the thread chain onto the throat plate by holding it with a feed dog behind the feeding direction of the stitch making zone, so that the thread chain cannot be made reliably. Accordingly, hitherto, in this kind of sewing machine, when the fabric reached the sewing end, the machine was stopped and the threads were trimmed, and after removing the sewn fabric, the forward end of the next fabric was fed on the throat plate beneath the presser foot, and the presser foot was lowered to resume the sewing operation, and therefore, it was impossible to sew by feeding the fabrics one after another by operating the sewing machine continuously.
In this kind of sewing machine, it is also proposed to form a thread chain by the sewing machine. An example is disclosed in Japanese unexamined patent publication number 3-23887 (U.S. Pat. No. 5,027,728), in which a thread brake device is positioned at the lower side of the stitch formation tongue formed by a U-shaped needle hole in the throat plate, and at the end of sewing, the same stitch as the one formed on the fabric is formed on the thread brake device to hold the thread chain and prevent its descent due to the lowering of the needles, and the formed thread chain is delivered by a rear feed dog disposed in its feed direction to make the thread chain.
Another sewing machine for forming a thread chain is proposed in Japanese patent publication number 57-58191 (U.S. Pat. No. 4,186,676), in which the thread tension of the right needle of two needles is released at the end of sewing, and the right needle thread does not resist a force pulling it toward the left needle thread by the looper thread, and the thread chain is sent out by the rear feed dog and an auxiliary feed member disposed at the delivery side of the needle hole.